System and method for reducing data loss during a serving cell change in a multi-flow HSDPA communication network

ABSTRACT

A method and apparatus for wireless communication may provide for reduced data loss during mobility events in a wireless communication network capable of downlink carrier aggregation. Some aspects of the disclosure provide for maintaining data corresponding to a flow in at least one buffer at a Node B when the Node B acts as a serving cell for the same UE both before and after a serving cell change. Another aspect of the disclosure provides for transferring buffered data from a Node B that acts as a serving cell for a UE before a serving cell change, to a Node B that acts as a serving cell for the UE after the serving cell change.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of provisionalpatent application No. 61/608,433, titled “System and Method forReducing Data Loss During a Serving Cell Change in a Multi-flow HSPDACommunication Network” and filed in the United States Patent andTrademark Office on Mar. 8, 2012, the entire content of which isincorporated herein by reference.

BACKGROUND

1. Field

Aspects of the present disclosure relate generally to wirelesscommunication systems, and more particularly, to serving cell changes ina system configured for downlink for carrier aggregation.

2. Background

Wireless communication networks are widely deployed to provide variouscommunication services such as telephony, video, data, messaging,broadcasts, and so on. Such networks, which are usually multiple accessnetworks, support communications for multiple users by sharing theavailable network resources. One example of such a network is the UMTSTerrestrial Radio Access Network (UTRAN). The UTRAN is the radio accessnetwork (RAN) defined as a part of the Universal MobileTelecommunications System (UMTS), a third generation (3G) mobile phonetechnology supported by the 3rd Generation Partnership Project (3GPP).The UMTS, which is the successor to Global System for MobileCommunications (GSM) technologies, currently supports various airinterface standards, such as Wideband-Code Division Multiple Access(W-CDMA), Time Division-Code Division Multiple Access (TD-CDMA), andTime Division-Synchronous Code Division Multiple Access (TD-SCDMA). TheUMTS also supports enhanced 3G data communications protocols, such asHigh Speed Packet Access (HSPA), which provides higher data transferspeeds and capacity to associated UMTS networks.

As the demand for mobile broadband access continues to increase,research and development continue to advance the UMTS technologies notonly to meet the growing demand for mobile broadband access, but toadvance and enhance the user experience with mobile communications.

As an example, Multi-Flow HSDPA has been recently introduced, in whichplural cells (provided by a single base station or plural base stations)can provide high-speed downlink communication to a mobile station, suchthat the mobile station is capable of aggregating the transmissions fromthose cells, within the same frequency carrier. As a relatively newsystem, various issues arise in this system that may not have beenaddressed in other downlink carrier aggregation systems such asDC-HSDPA. Thus, there is a need to identify and address issues relatingto system-level architecture, packet flow control, mobility, and others.

SUMMARY

The following presents a simplified summary of one or more aspects ofthe present disclosure, in order to provide a basic understanding ofsuch aspects. This summary is not an extensive overview of allcontemplated features of the disclosure, and is intended neither toidentify key or critical elements of all aspects of the disclosure norto delineate the scope of any or all aspect of the disclosure. Its solepurpose is to present some concepts of one or more aspects of thedisclosure in a simplified form as a prelude to the more detaileddescription that is presented later.

According to one embodiment, the disclosure provides a method ofwireless communication in which data loss during a serving cell changein a multi-flow HSPDA communication network is reduced. In the method, adownlink flow is transmitted from the RNC to a user equipment (UE)utilizing at least a first base station and a second base station toprovide a first serving cell and a second serving cell, respectively, tobe aggregated at the UE. The serving cells may be from one or moredifferent Node Bs and one or more different frequencies/carriers. Next,a serving cell change may be performed by the RNC where the first basestation or the second base station continues to act as a serving cell tothe UE. Data corresponding to the flow before the serving cell changemay be maintained within a queue at the acting serving cell fortransmission to the UE after the serving cell change. The cell qualitiesof the first serving cell and the second serving cell are ranked fromstrongest to weakest to select the acting serving cell. The actingserving cell is the primary serving cell and the non-selected servingcell is the secondary serving cell.

Prior to performing the serving cell change, a report from the UE may bereceived ranking the cell qualities of the first serving cell and thesecond serving cell, where the acting serving cell is selected based onstrongest cell quality from the ranked cell qualities; and wherein theacting serving cell is a primary serving cell and the non-selectedserving cell is the secondary serving cell. Additionally, the cellqualities of one or more neighboring serving cells, provided by one ormore base stations, may be ranked. A neighboring serving cell may beadded to an active set associated with the UE when the cell quality ofthe neighboring cell is stronger than the cell quality of the primaryserving cell or the secondary serving cell upon the occurrence of themobility event. When there is a serving change, instructions may be sentto the acting serving cell to maintain data corresponding to the flowbefore the serving cell change within a queue at the acting serving cellfor transmission to the UE after the serving cell change.

A mobility event may be a UE measurement of E_(c)/I₀ for a particularserving cell that reaches a predetermined threshold and maintains thepredetermined threshold for a predetermined time or a measurement ofE_(c)/I₀ for a particular serving cell falls that below a predeterminedthreshold and maintains the predetermined threshold for a predeterminedtime. Upon the occurrence of a mobility event, a neighboring servingcell from the one or more neighboring serving cells is added to anactive set associated with the UE when the cell quality of theneighboring cell is stronger than the cell quality of the primaryserving cell or the secondary serving cell.

According to one aspect, a primary serving cell change may be performedby replacing the primary serving cell with the neighboring serving cellwhen the cell quality of the neighboring serving cell is greater thanthe cell quality of the primary serving cell. The neighboring servingcell then becomes a new primary serving cell. Additionally a secondaryserving cell change may be performed by replacing the secondary cellwith the primary serving cell when the cell quality of the primaryserving cell is greater than the cell quality of the secondary servingcell. The primary serving cell becoming a new secondary serving cell.Data corresponding to the flow is maintained within a queue at the newprimary serving cell and the data corresponding to the flow is flushedfrom a queue at the secondary serving cell.

According to one aspect, a primary serving cell change may be performedby replacing the primary serving cell with the secondary serving cellwhen the cell quality of the secondary serving cell is greater than thecell quality of the primary serving cell. The secondary serving cellthen becomes a new primary serving cell. Additionally a secondaryserving cell change may be performed by replacing the secondary cellwith the neighboring serving cell when the cell quality of theneighboring serving cell is greater than the cell quality of thesecondary serving cell. The neighboring serving cell becomes a newsecondary serving cell. Data corresponding to the flow is maintainedwithin a queue at the new primary serving cell and the datacorresponding to the flow is flushed from a queue at the secondaryserving cell.

According to one aspect, a primary serving cell change may be performedby replacing the primary serving cell with the neighboring serving cellwhen the cell quality of the neighboring serving cell is greater thanthe cell quality of the primary serving cell. The neighboring servingcell then becomes a new primary serving cell. Data corresponding to theflow is maintained within a queue at the new primary serving cell andthe data corresponding to the flow is flushed from a queue at theprimary serving cell.

According to one aspect, the secondary serving cell is removed from theactive set associated with the UE when the cell quality of the secondserving cell is below a predetermined threshold. Data corresponding tothe flow is flushed from a queue at the secondary serving cell.

According to one aspect, a primary serving cell change may be performedby replacing the primary serving cell with the secondary serving cellwhen the cell quality of the secondary serving cell is greater than thecell quality of the primary serving cell. The secondary serving cellthen becomes a new primary serving cell. The primary serving cell isthen removed from the active set associated with the UE when the cellquality of the primary serving cell is below a predetermined threshold.Data corresponding to the flow is flushed from a queue at the primaryserving cell.

According to another embodiment, the disclosure provides an apparatusfor wireless communication. The apparatus may comprise means fortransmitting a downlink flow to user equipment (UE) utilizing at least afirst base station and a second base station to provide a first servingcell and a second serving cell, respectively, to be aggregated at theUE; means for performing a serving cell change, wherein the first basestation or the second base station continues to act as a serving cell tothe UE; and means for maintaining data corresponding to the flow beforethe serving cell change within a queue at the acting serving cell fortransmission to the UE after the serving cell change. Prior toperforming the serving cell change, the apparatus may further comprisemeans for receiving a report from the UE ranking cell qualities of thefirst serving cell and the second serving cell, where the acting servingcell is selected based on strongest cell quality from the ranked cellqualities; and wherein the acting serving cell is a primary serving celland the non-selected serving cell is the secondary serving cell. Thereport may further include ranking of the cell qualities of one or moreneighboring cells, provided by one or more base stations, upon anoccurrence of a mobility event; and wherein a neighboring cell is addedto an active set associated with the UE when the cell quality of theneighboring cell is stronger than the cell quality of the primaryserving cell or the secondary serving cell upon the occurrence of themobility event.

Additionally, the apparatus may include means for sending instructionsto the acting serving cell to maintain data corresponding to the flowbefore the serving cell change within a queue at the acting serving cellfor transmission to the UE after the serving cell change.

According to another embodiment, the disclosure provides a computerprogram product comprising a computer-readable medium operable on adevice configured to reduce data loss during a serving cell change in amulti-flow HSPDA communication network. The computer-readable storagemedium may comprise instructions for causing a computer to transmit adownlink flow to user equipment (UE) utilizing at least a first basestation and a second base station to provide a first serving cell and asecond serving cell, respectively, to be aggregated at the UE;instructions for causing a computer to perform a serving cell change,wherein the first base station or the second base station continues toact as a serving cell to the UE; and instructions for causing a computerto maintain data corresponding to the flow before the serving cellchange within a queue at the acting serving cell for transmission to theUE after the serving cell change. The computer-readable storage mediummay further comprise instructions for causing a computer to transmit adownlink flow to user equipment (UE) utilizing at least a first basestation and a second base station to provide a first serving cell and asecond serving cell, respectively, to be aggregated at the UE;instructions for causing a computer to perform a serving cell change,wherein the first base station or the second base station continues toact as a serving cell to the UE; and instructions for causing a computerto maintain data corresponding to the flow before the serving cellchange within a queue at the acting serving cell for transmission to theUE after the serving cell change.

According to another embodiment, the disclosure provides an apparatusconfigured to reduce data loss during a serving cell change in amulti-flow HSPDA communication network. The device may comprise at leaston processor and a memory coupled to the at least one processor which isconfigured to transmit a downlink flow to user equipment (UE) utilizingat least a first base station and a second base station to provide afirst serving cell and a second serving cell, respectively, to beaggregated at the UE; perform a serving cell change, wherein the firstbase station or the second base station continues to act as a servingcell to the UE; and maintain data corresponding to the flow before theserving cell change within a queue at the acting serving cell fortransmission to the UE after the serving cell change. The at least oneprocessor is further configured to rank cell qualities of the firstserving cell and the second serving cell to select the acting servingcell, the acting serving cell having the strongest cell quality, whereinthe acting serving cell is a primary serving cell and the non-selectedserving cell is the secondary serving cell; monitor one or moreneighboring serving cells, provided by one or more neighboring basestations, for a mobility event; and add a neighboring serving cell fromthe one or more neighboring serving cells to an active set associatedwith the UE when the cell quality of the neighboring cell is strongerthan the cell quality of the primary serving cell or the secondaryserving cell upon the occurrence of the mobility event.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating an example of a hardwareimplementation for an apparatus employing a processing system.

FIG. 2 is a block diagram conceptually illustrating an example of awireless communication system.

FIG. 3 is a conceptual diagram illustrating an example of a radioprotocol architecture for the user and control plane.

FIG. 4 is a conceptual diagram illustrating an example of an accessnetwork.

FIG. 5 is a call flow diagram illustrating an Event 1A procedure.

FIG. 6 is a call flow diagram illustrating an Event 1B procedure.

FIG. 7 is a call flow diagram illustrating an Event 1D procedure.

FIG. 8 is a schematic diagram illustrating a data flow in a conventionalHSDPA or DC-HSDPA network.

FIG. 9 is a schematic diagram illustrating a portion of a Multi-FlowHSDPA network.

FIG. 10 is a schematic diagram illustrating a data flow in a Multi-FlowHSDPA network.

FIG. 11 is a block diagram illustrating a portion of a user equipmentfor use in a Multi-Flow HSDPA network.

FIG. 12 is a simplified call flow diagram illustrating some of thesignaling among nodes for an Event 1D′, which is the measurement eventfor the best primary and secondary serving cells, according to oneexample.

FIG. 13 is a simplified call flow diagram illustrating some of thesignaling among nodes for an Event 1D, which is the measurement eventfor the best primary and secondary serving cells, according to oneexample.

FIG. 14 is a simplified call flow diagram illustrating some of thesignaling among nodes for an Event 1D, which is the measurement eventfor the best primary and secondary serving cells, according to oneexample.

FIG. 15 is a simplified call flow diagram illustrating some of thesignaling among nodes for an Event 1D, which is the measurement eventfor the best primary and secondary serving cells, according to oneexample.

FIG. 16 is a simplified call flow diagram illustrating some of thesignaling among nodes for an Event 1B, which is the measurement eventfor the best primary serving cell, according to one example.

FIG. 17 is a simplified call flow diagram illustrating some of thesignaling among nodes for an Event 1B, which is the measurement eventfor the best primary serving cell, according to one example.

FIG. 18 is a flow chart illustrating a process for reducing data lossduring a serving cell change in a Multi-flow HSPDA communicationnetwork.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of various configurations and isnot intended to represent the only configurations in which the conceptsdescribed herein may be practiced. The detailed description includesspecific details for the purpose of providing a thorough understandingof various concepts. However, it will be apparent to those skilled inthe art that these concepts may be practiced without these specificdetails. In some instances, well known structures and components areshown in block diagram form in order to avoid obscuring such concepts.

FIG. 1 is a conceptual diagram illustrating an example of a hardwareimplementation for an apparatus 100 employing a processing system 114.In accordance with various aspects of the disclosure, an element, or anyportion of an element, or any combination of elements may be implementedwith a processing system 114 that includes one or more processors 104.Examples of processors 104 include microprocessors, microcontrollers,digital signal processors (DSPs), field programmable gate arrays(FPGAs), programmable logic devices (PLDs), state machines, gated logic,discrete hardware circuits, and other suitable hardware configured toperform the various functionality described throughout this disclosure.

In this example, the processing system 114 may be implemented with a busarchitecture, represented generally by the bus 102. The bus 102 mayinclude any number of interconnecting buses and bridges depending on thespecific application of the processing system 114 and the overall designconstraints. The bus 102 links together various circuits including oneor more processors (represented generally by the processor 104), amemory 105, and computer-readable media (represented generally by thecomputer-readable medium 106). The bus 102 may also link various othercircuits such as timing sources, peripherals, voltage regulators, andpower management circuits, which are well known in the art, andtherefore, will not be described any further. A bus interface 108provides an interface between the bus 102 and a transceiver 110. Thetransceiver 110 provides a means for communicating with various otherapparatus over a transmission medium. Depending upon the nature of theapparatus, a user interface 112 (e.g., keypad, display, speaker,microphone, joystick) may also be provided.

The processor 104 is responsible for managing the bus 102 and generalprocessing, including the execution of software stored on thecomputer-readable medium 106. The software, when executed by theprocessor 104, causes the processing system 114 to perform the variousfunctions described infra for any particular apparatus. Thecomputer-readable medium 106 may also be used for storing data that ismanipulated by the processor 104 when executing software.

One or more processors 104 in the processing system may executesoftware. Software shall be construed broadly to mean instructions,instruction sets, code, code segments, program code, programs,subprograms, software modules, applications, software applications,software packages, routines, subroutines, objects, executables, threadsof execution, procedures, functions, etc., whether referred to assoftware, firmware, middleware, microcode, hardware descriptionlanguage, or otherwise. The software may reside on a computer-readablemedium 106. The computer-readable medium 106 may be a non-transitorycomputer-readable medium. A non-transitory computer-readable mediumincludes, by way of example, a magnetic storage device (e.g., hard disk,floppy disk, magnetic strip), an optical disk (e.g., a compact disc (CD)or a digital versatile disc (DVD)), a smart card, a flash memory device(e.g., a card, a stick, or a key drive), a random access memory (RAM), aread only memory (ROM), a programmable ROM (PROM), an erasable PROM(EPROM), an electrically erasable PROM (EEPROM), a register, a removabledisk, and any other suitable medium for storing software and/orinstructions that may be accessed and read by a computer. Thecomputer-readable medium may also include, by way of example, a carrierwave, a transmission line, and any other suitable medium fortransmitting software and/or instructions that may be accessed and readby a computer. The computer-readable medium 106 may reside in theprocessing system 114, external to the processing system 114, ordistributed across multiple entities including the processing system114. The computer-readable medium 106 may be embodied in a computerprogram product. By way of example, a computer program product mayinclude a computer-readable medium in packaging materials. Those skilledin the art will recognize how best to implement the describedfunctionality presented throughout this disclosure depending on theparticular application and the overall design constraints imposed on theoverall system.

The various concepts presented throughout this disclosure may beimplemented across a broad variety of telecommunication systems, networkarchitectures, and communication standards. Referring now to FIG. 2, asan illustrative example without limitation, various aspects of thepresent disclosure are illustrated with reference to a Universal MobileTelecommunications System (UMTS) system 200. A UMTS network includesthree interacting domains: a core network 204, a radio access network(RAN) (e.g., the UMTS Terrestrial Radio Access Network (UTRAN) 202), anda user equipment (UE) 210. Among several options available for a UTRAN202, in this example, the illustrated UTRAN 202 may employ a W-CDMA airinterface for enabling various wireless services including telephony,video, data, messaging, broadcasts, and/or other services. The UTRAN 202may include a plurality of Radio Network Subsystems (RNSs) such as anRNS 207, each controlled by a respective Radio Network Controller (RNC)such as an RNC 206. Here, the UTRAN 202 may include any number of RNCs206 and RNSs 207 in addition to the illustrated RNCs 206 and RNSs 207.The RNC 206 is an apparatus responsible for, among other things,assigning, reconfiguring, and releasing radio resources within the RNS207. The RNC 206 may be interconnected to other RNCs (not shown) in theUTRAN 202 through various types of interfaces such as a direct physicalconnection, a virtual network, or the like using any suitable transportnetwork.

The geographic region covered by the RNS 207 may be divided into anumber of cells, with a radio transceiver apparatus serving each cell. Aradio transceiver apparatus is commonly referred to as a Node B in UMTSapplications, but may also be referred to by those skilled in the art asa base station (BS), a base transceiver station (BTS), a radio basestation, a radio transceiver, a transceiver function, a basic serviceset (BSS), an extended service set (ESS), an access point (AP), or someother suitable terminology. For clarity, three Node Bs 208 are shown ineach RNS 207; however, the RNSs 207 may include any number of wirelessNode Bs. The Node Bs 208 provide wireless access points to a corenetwork 204 for any number of mobile apparatuses. Examples of a mobileapparatus include a cellular phone, a smart phone, a session initiationprotocol (SIP) phone, a laptop, a notebook, a netbook, a smartbook, apersonal digital assistant (PDA), a satellite radio, a globalpositioning system (GPS) device, a multimedia device, a video device, adigital audio player (e.g., MP3 player), a camera, a game console, orany other similar functioning device. The mobile apparatus is commonlyreferred to as user equipment (UE) in UMTS applications, but may also bereferred to by those skilled in the art as a mobile station (MS), asubscriber station, a mobile unit, a subscriber unit, a wireless unit, aremote unit, a mobile device, a wireless device, a wirelesscommunications device, a remote device, a mobile subscriber station, anaccess terminal (AT), a mobile terminal, a wireless terminal, a remoteterminal, a handset, a terminal, a user agent, a mobile client, aclient, or some other suitable terminology. In a UMTS system, the UE 210may further include a universal subscriber identity module (USIM) 211,which contains a user's subscription information to a network. Forillustrative purposes, one UE 210 is shown in communication with anumber of the Node Bs 208. The downlink (DL), also called the forwardlink, refers to the communication link from a Node B 208 to a UE 210 andthe uplink (UL), also called the reverse link, refers to thecommunication link from a UE 210 to a Node B 208.

The core network 204 can interface with one or more access networks,such as the UTRAN 202. As shown, the core network 204 is a UMTS corenetwork. However, as those skilled in the art will recognize, thevarious concepts presented throughout this disclosure may be implementedin a RAN, or other suitable access network, to provide UEs with accessto types of core networks other than UMTS networks.

The illustrated UMTS core network 204 includes a circuit-switched (CS)domain and a packet-switched (PS) domain. Some of the circuit-switchedelements are a Mobile services Switching Centre (MSC), a VisitorLocation Register (VLR), and a Gateway MSC (GMSC). Packet-switchedelements include a Serving GPRS Support Node (SGSN) and a Gateway GPRSSupport Node (GGSN). Some network elements, like EIR, HLR, VLR, and AuCmay be shared by both of the circuit-switched and packet-switcheddomains.

In the illustrated example, the core network 204 supportscircuit-switched services with a MSC 212 and a GMSC 214. In someapplications, the GMSC 214 may be referred to as a media gateway (MGW).One or more RNCs, such as the RNC 206, may be connected to the MSC 212.The MSC 212 is an apparatus that controls call setup, call routing, andUE mobility functions. The MSC 212 also includes a visitor locationregister (VLR) that contains subscriber-related information for theduration that a UE is in the coverage area of the MSC 212. The GMSC 214provides a gateway through the MSC 212 for the UE to access acircuit-switched network 216. The GMSC 214 includes a home locationregister (HLR) 215 containing subscriber data, such as the datareflecting the details of the services to which a particular user hassubscribed. The HLR is also associated with an authentication center(AuC) that contains subscriber-specific authentication data. When a callis received for a particular UE, the GMSC 214 queries the HLR 215 todetermine the UE's location and forwards the call to the particular MSCserving that location.

The illustrated core network 204 also supports packet-switched dataservices with a serving GPRS support node (SGSN) 218 and a gateway GPRSsupport node (GGSN) 220. General Packet Radio Service (GPRS) is designedto provide packet-data services at speeds higher than those availablewith standard circuit-switched data services. The GGSN 220 provides aconnection for the UTRAN 202 to a packet-based network 222. Thepacket-based network 222 may be the Internet, a private data network, orsome other suitable packet-based network. The primary function of theGGSN 220 is to provide the UEs 210 with packet-based networkconnectivity. Data packets may be transferred between the GGSN 220 andthe UEs 210 through the SGSN 218, which performs primarily the samefunctions in the packet-based domain as the MSC 212 performs in thecircuit-switched domain.

The UTRAN air interface may be a spread spectrum Direct-Sequence CodeDivision Multiple Access (DS-CDMA) system, such as one utilizing theW-CDMA standards. The spread spectrum DS-CDMA spreads user data throughmultiplication by a sequence of pseudorandom bits called chips. TheW-CDMA air interface for the UTRAN 202 is based on such DS-CDMAtechnology and additionally calls for a frequency division duplexing(FDD). FDD uses a different carrier frequency for the uplink (UL) anddownlink (DL) between a Node B 408 and a UE 210. Another air interfacefor UMTS that utilizes DS-CDMA, and uses time division duplexing (TDD),is the TD-SCDMA air interface. Those skilled in the art will recognizethat although various examples described herein may refer to a W-CDMAair interface, the underlying principles are equally applicable to aTD-SCDMA air interface or any other suitable air interface.

A high speed packet access (HSPA) air interface includes a series ofenhancements to the 3G/W-CDMA air interface between the UE 210 and theUTRAN 202, facilitating greater throughput and reduced latency forusers. Among other modifications over prior standards, HSPA utilizeshybrid automatic repeat request (HARQ), shared channel transmission, andadaptive modulation and coding. The standards that define HSPA includeHSDPA (high speed downlink packet access) and HSUPA (high speed uplinkpacket access, also referred to as enhanced uplink or EUL).

In a wireless telecommunication system, the communication protocolarchitecture may take on various forms depending on the particularapplication. For example, in a 3GPP UMTS system, the signaling protocolstack is divided into a Non-Access Stratum (NAS) and an Access Stratum(AS). The NAS provides the upper layers, for signaling between the UE210 and the core network 204 (referring to FIG. 2), and may includecircuit switched and packet switched protocols. The AS provides thelower layers, for signaling between the UTRAN 202 and the UE 210, andmay include a user plane and a control plane. Here, the user plane ordata plane carries user traffic, while the control plane carries controlinformation (i.e., signaling).

Turning to FIG. 3, the AS is shown with three layers: Layer 1, Layer 2,and Layer 3. Layer 1 is the lowest layer and implements various physicallayer signal processing functions. Layer 1 will be referred to herein asthe physical layer 306. The data link layer, called Layer 2 (L2 layer)308 is above the physical layer 306 and is responsible for the linkbetween the UE and Node B over the physical layer 306.

At Layer 3, the RRC layer 316 handles the control plane signalingbetween the UE and the RNC. RRC layer 316 includes a number offunctional entities for routing higher layer messages, handlingbroadcast and paging functions, establishing and configuring radiobearers, etc.

In the illustrated air interface, the L2 layer 308 is split intosublayers. In the control plane, the L2 layer 308 includes twosublayers: a medium access control (MAC) sublayer 310 and a radio linkcontrol (RLC) sublayer 312. In the user plane, the L2 layer 308additionally includes a packet data convergence protocol (PDCP) sublayer314. Although not shown, the UE may have several upper layers above theL2 layer 308 including a network layer (e.g., IP layer) that isterminated at a PDN gateway on the network side, and an applicationlayer that is terminated at the other end of the connection (e.g., farend UE, server, etc.).

The PDCP sublayer 314 provides multiplexing between different radiobearers and logical channels. The PDCP sublayer 314 also provides headercompression for upper layer data packets to reduce radio transmissionoverhead, security by ciphering the data packets, and handover supportfor UEs between Node Bs.

The RLC sublayer 312 generally supports acknowledged, unacknowledged,and transparent mode data transfers, and provides segmentation andreassembly of upper layer data packets, retransmission of lost datapackets, and reordering of data packets to compensate for out-of-orderreception due to a hybrid automatic repeat request (HARQ). That is, theRLC sublayer 312 includes a retransmission mechanism that may requestretransmissions of failed packets. Here, if the RLC sublayer 312 isunable to deliver the data correctly after a certain maximum number ofretransmissions or an expiration of a transmission time, upper layersare notified of this condition and the RLC SDU may be discarded.

Further, the RLC sublayer at the RNC 206 (see FIG. 2) may include a flowcontrol function for managing the flow of RLC protocol data units(PDUs). For example, the RNC may determine an amount of data to send toa Node B, and may manage details of that allocation including dividingthe data into batches and distributing those batches or packets amongmultiple Node Bs in the case of downlink aggregation, e.g., in aDC-HSDPA system or a Multi-Point HSDPA system.

The MAC sublayer 310 provides multiplexing between logical and transportchannels. The MAC sublayer 310 is also responsible for allocating thevarious radio resources (e.g., resource blocks) in one cell among theUEs, as well as HARQ operations. The MAC sublayer 310 can includevarious MAC entities, including but not limited to a MAC-d entity andMAC-hs/ehs entity.

The UTRAN 202 is one example of a RAN that may be utilized in accordancewith the present disclosure. Referring to FIG. 4, by way of example andwithout limitation, a simplified schematic illustration of a RAN 400 ina UTRAN architecture is illustrated. The system includes multiplecellular regions (cells), including cells 402, 404, and 406, each ofwhich may include one or more sectors. In the present disclosure, theterm “cells” may refer generally to communication channels between UEsand Node Bs, and may include sectors depending on the context. Cells maybe defined geographically, e.g., by coverage area, and/or may be definedin accordance with a frequency, scrambling code, etc. That is, theillustrated geographically-defined cells 402, 404, and 406 may each befurther divided into a plurality of cells, e.g., by utilizing differentscrambling codes. For example, cell 404 a may utilize a first scramblingcode, and cell 404 b, while in the same geographic region and served bythe same Node B 444, may be distinguished by utilizing a secondscrambling code.

In a cell that is divided into sectors, the multiple sectors within thecell can be formed by groups of antennas, with each antenna responsiblefor communication with UEs in a portion of the cell. For example, incell 402, antenna groups 412, 414, and 416 may each correspond to adifferent sector. In cell 404, antenna groups 418, 420, and 422 eachcorrespond to a different sector. In cell 406, antenna groups 424, 426,and 428 each correspond to a different sector.

The cells 402, 404 and 406 may include several UEs that may be incommunication with one or more sectors of each cell 402, 404 or 406. Forexample, UEs 430 and 432 may be in communication with Node B 442, UEs434 and 436 may be in communication with Node B 444, and UEs 438 and 440may be in communication with Node B 446. Here, each Node B 442, 444, 446is configured to provide an access point to a core network 204 (see FIG.2) for all the UEs 430, 432, 434, 436, 438, 440 in the respective cells402, 404, and 406.

During a call with the source cell 404 a, or at any other time, the UE436 may monitor various parameters of the source cell 404 a as well asvarious parameters of neighboring cells such as cells 404 b, 406, and402. Further, depending on the quality of these parameters, the UE 436may maintain some level of communication with one or more of theneighboring cells. During this time, the UE 436 may maintain an ActiveSet, that is, a list of cells that the UE 436 is simultaneouslyconnected to (i.e., the UTRA cells that are currently assigning adownlink dedicated physical channel DPCH or fractional downlinkdedicated physical channel F-DPCH to the UE 436 may constitute theActive Set). Here, the cells in the Active Set can form a soft handoverconnection to the UE. The UE may additionally include a neighbor set ormonitored set, including a list of cells that the UE may measure, butwhose signal strength is not high enough to be included in the ActiveSet.

Management of the Active Set can be enabled through the use of certainRadio Resource Control (RRC) messages between the RNC and UE. Forexample, the selection of cells to include in the Active Set may dependon certain UE measurements, which may be configured by the network in asystem information block (SIB).

For example, the UE may measure a ratio between the signal strength andthe noise floor (E_(c)/I₀) of a pilot signal (e.g., a common pilotchannel CPICH) transmitted by each cell in the UE's monitored set. Thatis, the UE may determine the E_(c)/I₀ for nearby cells, and may rank thecells based on these measurements.

When the ranking of a cell changes, or if any other reporting trigger ormeasurement event (discussed in further detail below) occurs, the UE maysend certain RRC messages to the RNC to report this event. Thus, the RNCmay make a decision to alter the Active Set for the UE, and send an RRCmessage (i.e., an Active Set Update message) to the UE indicating achange in the Active Set. The RNC may then communicate with therespective Node B or Node Bs, e.g., over an Iub interface utilizing NodeB Application Part (NBAP) signaling to configure the cells forcommunication with the UE. Finally, the RNC may communicate with the UEutilizing further RRC messages, such as a Physical ChannelReconfiguration (PCR) message, with an RRC response from the UE of PCRComplete indicating success of the reconfiguration.

One reporting trigger may result when a primary CPICH enters thereporting range for the UE. That is, when the E_(c)/I₀ for a particularcell reaches a particular or predetermined threshold (e.g., a certainnumber of dB below the E_(c)/I₀ of the primary serving cell) andmaintains that level for a certain time such that it may be appropriateto add the cell to the Active Set a reporting event called Event 1A mayoccur. FIG. 5 is a simplified call flow diagram illustrating some of thesignaling among nodes for Event 1A. In this and the call flow diagramsto follow, time generally proceeds from the top of the diagram to thebottom, although in many cases the illustrated sequence of signals isnot intended to be the only possible sequence, and other sequences maybe utilized in accordance with various aspects of the presentdisclosure. Further, the sequence numbers at the right-hand side of thecall flow diagrams are merely placed to ease a description, and eachtime number may represent any reasonable span of time from an instant toseveral seconds.

In the illustrated example, at time (1) the UE 502 has determined that ameasurement of Cell 2 has increased above a threshold and entered areporting range, and thus, the UE 502 may transmit an RRC MeasurementReport message including Event 1A and identifying Cell 2, 506. Inresponse, at time (2) the RNC 508 may communicate with Cell 2, 506, overthe Iub interface utilizing NBAP signaling to set up a radio link withthe UE 502. At time (3), the RNC 508 may send an RRC Active Set Updatemessage to the UE 502 indicating to add Cell 2, 506, to its Active Set.The UE 502 may respond at time (4) with an RRC Active Set UpdateComplete message to the RNC 508, completing the Active Set update.

Another reporting trigger may result when a primary CPICH leaves thereporting range. That is, when the E_(c)/I₀ for a particular cell fallsbelow a particular or predetermined threshold (e.g., a certain number ofdB below the E_(c)/I₀ of the primary serving cell), and maintains thatlevel for a certain time such that it may be appropriate to remove thecell from the Active Set a reporting event called Event 1B may occur.FIG. 6 is a simplified call flow diagram illustrating some of thesignaling among nodes for Event 1B. In the illustrated example, at time(1) the UE 502 has determined that Cell 2, 506 has left the reportingrange. Thus, the UE 502 may transmit the RRC Measurement Report messageincluding Event 1B and identifying Cell 2 506. In response, at time (2)the RNC 508 may transmit an RRC Active Set Update message to the UE 502indicating to remove Cell 2 506 from the Active Set. At time (3), the UE502 may then respond with an RRC Active Set Update Complete message tothe RNC 508, indicating that the Active Set is updated. At time (4) theRNC 508 may then transmit NBAP signaling over the Iub interface to Cell2 506 to delete the radio link between Cell 2 506 and the UE 502.

Another reporting trigger may result when the Active Set is full, and aprimary CPICH of a candidate cell outside the Active Set exceeds that ofthe weakest cell in the Active Set, such that it may be appropriate toreplace the weakest cell in the Active Set with the candidate cell.Here, a reporting event called Event 1C may occur, causing a combinedradio link addition and removal. Because the Event 1C is substantially acombination of the Event 1A and Event 1B, and is known to those skilledin the art, a detailed description is not included herein.

In Release 5 of the 3GPP family of standards, High Speed Downlink PacketAccess (HSDPA) was introduced. HSDPA utilizes as its transport channelthe high-speed downlink shared channel (HS-DSCH), which may be shared byseveral UEs. The HS-DSCH is implemented by three physical channels: thehigh-speed physical downlink shared channel (HS-PDSCH), the high-speedshared control channel (HS-SCCH), and the high-speed dedicated physicalcontrol channel (HS-DPCCH).

The HS-DSCH may be associated with one or more HS-SCCH. The HS-SCCH is aphysical channel that may be utilized to carry downlink controlinformation related to the transmission of HS-DSCH. The UE maycontinuously monitor the HS-SCCH to determine when to read its data fromthe HS-DSCH, and the modulation scheme used on the assigned physicalchannel.

The HS-PDSCH is a physical channel that may be shared by several UEs.The HS-PDSCH may support quadrature phase shift keying (QPSK) and16-quadrature amplitude modulation (16-QAM) and multi-code transmission.

The HS-DPCCH is an uplink physical channel that may carry feedback fromthe UE to assist the Node B in its scheduling algorithm. The feedbackmay include a channel quality indicator (CQI) and a positive or negativeacknowledgement (ACK/NAK) of a previous HS-DSCH transmission.

One difference on the downlink between HSDPA and the previouslystandardized circuit-switched air-interface is the absence of softhandover in HSDPA. This means that HSDPA channels are transmitted to theUE from a single cell called the HSDPA serving cell. As the user moves,or as one cell becomes preferable to another, the HSDPA serving cell maychange. Still, the UE may be in soft handover on the associated DPCH,receiving the same information from plural cells.

In Rel. 5 HSDPA, at any instance a UE has one serving cell, that beingthe strongest cell in the Active Set as according to the UE measurementsof E_(c)/I₀. According to mobility procedures defined in Rel. 5 of 3GPPTS 25.331, the Radio Resource Control (RRC) signaling messages forchanging the HSPDA serving cell are transmitted from the current HSDPAserving cell (i.e., the source cell), and not the cell that the UEreports as being the stronger cell (i.e., the target cell).

That is, in addition to the reporting triggers dealing with Event 1A andEvent 1B, described above, for HSDPA another reporting trigger mayresult when a neighbor cell (which may or may not be within the ActiveSet) exceeds the quality of the serving HS-DSCH cell according to the UEmeasurements of E_(c)/I₀. In this case it may be appropriate tore-select the serving HS-DSCH cell. FIG. 7 is a simplified call flowdiagram illustrating some of the signaling among nodes for Event 1D,which is the measurement event for the best serving HS-DSCH cell. In theillustrated example, at time (1) Cell 1 504 begins as the servingHS-DSCH cell. At time (2), the UE 502 may determine that Cell 2, 506,exceeds Cell 1, 504 in terms of its CPICH E_(c)/I₀. Thus, the UE 502 maytransmit an RRC Measurement Report message including Event 1D andidentifying Cell 2 506. In response, at time (3) the RNC 508 maytransmit signaling to Cell 2 506 over the Iub interface utilizing NBAPsignaling to set up a radio link with the UE 502. At time (4), the RNC508 may send an RRC Transport Channel Reconfiguration Request to the UE502 indicating a serving cell change, such that Cell 2, 506, will be thenew serving HS-DSCH cell. The UE 502 may then respond at time (5) withan RRC Transport Channel Reconfiguration Complete message to the RNC508. At time (6), the RNC may utilize NBAP signaling to delete the radiolink setup at Cell 1 504. Thus, at time (7) HSDPA service can begin withthe new serving HS-DSCH cell, i.e., Cell 2, 506.

Although some differences may exist for inter-frequency handovers, asknown to those having ordinary skill in the art, those are largelyoutside the scope of the present disclosure and are not discussedherein.

FIG. 8 is a schematic illustration of a downlink path in an HSDPAnetwork between an RNC 802 and a UE 806, passing through a Node B 804,showing some of the sublayers at the respective nodes. Here, the RNC 802may be the same as the RNC 206 illustrated in FIG. 2; the Node B 804 maybe the same as the Node B 208 illustrated in FIG. 2; and the UE 806 maybe the same as the UE 210 illustrated in FIG. 2. The RNC 802 housesprotocol layers from MAC-d and above, including for example the RLCsublayer. For the high speed channels, a MAC-hs/ehs layer is housed inthe Node B 804. Further a PHY layer at the Node B 804 provides an airinterface for communicating with a PHY layer at the UE 806, e.g., overan HS-DSCH.

From the UE 806 side, a MAC-d entity is configured to control access toall the dedicated transport channels, to a MAC-c/sh/m entity, and to theMAC-hs/ehs entity. Further, from the UE 806 side, the MAC-hs/ehs entityis configured to handle the HSDPA specific functions and control accessto the HS-DSCH transport channel. Upper layers configure which of thetwo entities, MAC-hs or MAC-ehs, is to be applied to handle HS-DSCHfunctionality.

Release 8 of the 3GPP standards brought dual cell HSDPA (DC-HSDPA),which enables a UE to aggregate dual adjacent 5-MHz downlink carriers.The dual carrier approach provides higher downlink data rates and betterefficiency at multicarrier sites. Generally, DC-HSDPA utilizes a primary(anchor) carrier and a secondary carrier, where the primary carrierprovides the channels for downlink data transmission and the channelsfor uplink data transmission, and the secondary carrier provides asecond set of HS-PDSCHs and HS-SCCHs for downlink communication.

In DC-HSDPA, the downlink carriers are generally provided by the samecell, and mobility is based on the primary carrier. Thus, the mobilityprocedures are largely the same as those utilized for single-carrierHSDPA. However, additional information may be included in the RRChandover messaging to indicate whether to use single or dual carriersafter a handover to a target cell, since not all cells may supportDC-HSDPA. Here, the information element (IE) in the RRC message for ahandover to a DC-HSDPA-capable Node B can include information about thefrequency or carrier for the secondary carrier at the target cell.

According to some aspects of the present disclosure, another form ofcarrier aggregation, which may be referred to as soft aggregation,provides for downlink carrier aggregation wherein the respectivedownlink carriers utilize the same frequency carrier. Soft aggregationstrives to realize similar gains to DC-HSDPA in a single-carriernetwork.

FIG. 9 illustrates an exemplary system for soft aggregation inaccordance with some aspects of the present disclosure. In FIG. 9, theremay be a geographic overlap between two or more cells 914 and 916, suchthat a UE 910 may be served, at least for a certain period of time, bythe multiple cells. Thus, a wireless telecommunication system inaccordance with the present disclosure may provide HSDPA service from aplurality of cells on a single frequency channel, such that a UE mayperform aggregation. Here, the UE may aggregate downlinks from a primaryserving cell and at least one secondary serving cell. For example, asetup utilizing two or more cells may be referred to as Multi-Flow HSDPA(MF-HSDPA), coordinated multi-point HSDPA (CoMP HSDPA), or simplymulti-point HSDPA. One particular configuration utilizing two cells eachproviding HSDPA data on the same frequency carrier is sometimes referredto as single frequency dual cell HSDPA (SF-DC-HSDPA). However, otherterminology may freely be utilized. In this way, users at cellboundaries, as well as the overall system, may benefit from a highthroughput. In various examples, the different cells may be provided bythe same Node B, or the different cells may be provided by disparateNode Bs. That is, the cells may be from 1 or more different Node Bs and1 or more different frequencies/carriers.

In the scheme illustrated in FIG. 9, two Node Bs 902 and 904 eachprovide a downlink cell 906 and 908, respectively, wherein the downlinkcells are in substantially the same carrier frequency. Of course, asalready described, in another example, both downlink cells 906 and 908may be provided from different sectors of the same Node B. The UE 910receives and aggregates the downlink cells and provides an uplinkchannel 912, which may be received by one or both Node Bs 902 and 904.The uplink channel 912 from the UE 910 may provide feedback information,e.g., corresponding to the downlink channel state for the correspondingdownlink cells 906 and 908.

As compared to the conventional HSDPA-capable UE 806 described above inrelation to FIG. 8, a DC-HSDPA-capable UE has two receive chains, eachof which may be used to receive HS data from a different carrier. In aMulti-Flow HSDPA-capable UE, if the plural receive chains are made toreceive HS data from different cells, at least some the benefits fromaggregation can be realized in a single-carrier network.

In some aspects of the present disclosure, the cells being aggregatedmay be restricted to cells in the UE's Active Set. These cells may bethe strongest cells in the Active Set, determined in accordance with thedownlink channel quality. If the strongest cells reside in differentNode B sites, this scheme may be called ‘soft aggregation’. If thestrongest cells to be aggregated reside in the same Node B site, thisscheme may be called ‘softer aggregation.’

Softer aggregation is relatively straightforward to evaluate andimplement. However, since the percentage of UEs in softer handover maybe limited, the gain from softer aggregation may correspondingly belimited as well. Compared to softer aggregation, soft aggregation hasthe potential to offer a greater benefit. However, there are variousconcerns related to uplink overhead channel performance and out-of-orderdelivery.

In a conventional DC-HSDPA or Multi-Flow HSDPA system wherein both cellsare provided by a single Node B (i.e., softer aggregation), the twocells may share the same MAC-ehs entity in much the same way as theconventional HSDPA system illustrated in FIG. 8. In that configuration,because the downlink data comes to the UE 806 from a single Node B site,the RLC entity at the UE 806 may generally assume that the packets aresent in order in accordance with their respective RLC sequence numbers.Thus, any gap in sequence numbers in received packets can be understoodto be caused by a packet failure, and the RLC entity at the RNC maysimply retransmit all packets corresponding to the missing sequencenumbers.

In an aspect of the present disclosure, as illustrated in FIG. 10, anRNC 1002 may include a multi-link RLC sublayer that provides packets toa plurality of Node Bs 1004 and 1006, which each provide downlinkHS-transmissions to a UE 1008. Thus, the UE may be enabled for downlinkaggregation, e.g., Multi-Flow HSDPA.

Here, the UE 1008 may include a plurality of MAC entities, each of theplurality of MAC entities corresponding to a different serving cell(e.g., a primary serving cell and a secondary serving cell) fromcorresponding Node B sites. For example, one MAC entity in the UE 1008may correspond to the first Node B 1004 providing a primary servingcell, and a second MAC entity in the UE 1008 may correspond to thesecond Node B 1006 providing a secondary serving cell. Of course, forvarious reasons, the pairing of a particular MAC entity with aparticular Node B may change over time, and the illustration is only onepossible example.

Thus, the RNC 1002 may include a multi-link RLC sublayer, wherein a flowcontrol algorithm allocates packets for the UE 1008 among the pluralityof cells (e.g., at Node Bs 1004 and 1006) utilizing a plurality of RLClinks, e.g., over Iub interfaces.

FIG. 11 is a simplified block diagram illustrating some of thecomponents of an exemplary UE 1110 for use in a Multi-Flow HSDPA networkin accordance with some aspects of the present disclosure. In theillustration, the UE 1110 includes two receive antennas for receivingrespective downlink signals, as in a SF-DC or DF-DC HSDPA network.However, within the scope of the present disclosure, a UE 1110 mayinclude any number of antennas for receiving downlink signals in thesame carrier frequency or in any suitable number of different carrierfrequencies. Further, the illustrated UE 1110 shows an example for asingle-band network. In a multi-carrier network where the UE isconfigured to receive at least one carrier in each of two or more bands,the UE would further include blocks such as a diplexer, as is known tothose of ordinary skill in the art.

Coupled to each of the antennas may be a respective RF front end 1102,1104. The RF front end may include such functional blocks as RFdown-conversion, low-pass filtering, etc. The RF front end then feedsinto an analog to digital converter 1106 and 1108, which may transformthe received downlink channels to the digital domain to be furtherprocessed by a base-band unit or BBU 1110. The BBU 1110 may include suchfunctional blocks as carrier/antenna separation, a base-band detector,and a base-band decoder, configured to provide the received transportblocks to a processor 1112 to be further processed in accordance withthe received information. In some examples, the processor 1112 may bethe same as the processing system 114 illustrated in FIG. 1. Theprocessor 1112 may additionally be coupled to one or more transmitters1114, which may utilize one or more of the UE's antennas as managed by asuitable duplexer. The processor 1112 may additionally utilize a memory1118 for storing information useful for the processing of theinformation.

Mobility for the Multi-Flow HSDPA system as illustrated in FIG. 9 can besomewhat more involved than mobility for an HSDPA or a DC-HSDPA system,since those systems generally provide the respective HS downlinkchannels from a single Node B site, whereas for Multi-Flow HSDPA theremay be an active link with a plurality of Node B sites.

As described above, in a conventional HSDPA or DC-HSDPA network, the UEis provided the high-speed downlink by a single serving cell (referredto as the serving HS-DSCH cell). Prior to a handover or serving cellchange, the serving HS-DSCH cell may be referred to as the source cell.After the serving cell change, when the serving HS-DSCH cell is replaced(e.g., through Event 1D) by another cell, which may be referred to asthe target cell, both the network and the UE generally flush anybuffered data corresponding to the flow. For example, data in the HARQbuffer at the MAC layer may be flushed. This leads to data loss andgenerally results in an extra retransmission of the lost data by theupper layers (e.g., the RLC or TCP).

Similarly, in conventional inter-Node B SF-DC HSDPA, when anchorswitching occurs (e.g., when the primary serving cell and the secondaryserving cell swap), the HARQ buffer at the network side and the UE sidemay be flushed, leading to RLC/TCP retransmission.

Therefore, various aspects of the present disclosure provide a servingcell procedure operable in a wireless communication network configuredfor downlink carrier aggregation, e.g., a Multi-Flow HSDPA network,capable to reduce or eliminate the data loss described above during aserving cell change procedure.

For example, in some aspects of the present disclosure, when anchorswitching occurs in a Multi-Flow HSDPA network, the network and the UEmay maintain the data in HARQ buffer. This contrasts from theconventional networks, wherein this data is generally flushed, asdescribed above. In a further aspect of the present disclosure, for thebuffered data packets, the HARQ ID and TSN remain the same.

In this way, by maintaining the buffered data, all the data in HARQbuffer can be transmitted to the UE from the new serving cells after theanchor switching. Thus, the data loss associated with the serving cellchange can be reduced or eliminated.

In another aspect of the disclosure relating to the anchor switchingscenario described above, rather than maintaining the data in therespective buffers at the time of the anchor switch, the data in therespective buffers of the source cell and the target cell may beswapped. That is, the data buffered at the source cell may betransmitted to the target cell, and the data buffered at the target cellmay be transmitted to the source cell. As an illustrative example,referring to FIG. 9, the source Node B 902 may transmit its buffereddata over the Iub interface 920 to the RNC 918, and the RNC 918 mayaccordingly forward the information over the Iub interface 922 to thetarget Node B 904. Further, the target Node B 904 may transmit itsbuffered data over the Iub interface 922 to the RNC 918, and the RNC 918may accordingly forward the information over the Iub interface 920 tothe source Node B 902. In this way, following the anchor switch, theNode Bs 902 and 904 may accordingly transmit the data to the UE 910 in away that maintains the flow corresponding to the anchor carrier and thesecondary carrier.

In a further aspect of the present disclosure, the above processes canbe generalized to apply to other mobility events in a network configuredfor downlink carrier aggregation, e.g., a Multi-Flow HSDPA network. Forexample, a paradigm may be established for a serving cell change,wherein buffered data at the Node B and at the UE may be maintained,rather than flushed, if the Node B remains as a serving HS-DSCH cellfollowing the serving cell change. However, if the Node B is removed asa serving HS-DSCH cell during the course of the serving cell changeprocedure, the buffered data may be flushed. In another example, thebuffered data may be transferred to another Node B, e.g., utilizingbackhaul connections, wherein the Node B to which the buffered data istransferred, performs as a serving HS-DSCH cell following the servingcell change.

Such a paradigm can apply when removing a primary serving HS-DSCH cellor a secondary serving HS-DSCH cell from the set of serving cells; orwhen adding a primary serving HS-DSCH cell or a secondary servingHS-DSCH cell from the set of serving cells. Of course, in variousexamples, there may be any number of serving HS-DSCH cells, providing adownlink carrier to the UE in any one or more carrier frequencies,according to the capabilities of the UE and the network.

Table 1 below illustrates a set of mobility events for an exemplarySF-DC HSDPA network, wherein two downlink carriers are provided at anygiven time by two disparate Node Bs, utilizing the same carrierfrequency. However, this is by way of example only and the serving cellsmay be from 1 or more different Node Bs and 1 or more differentfrequencies/carriers.

In the table, three different Node Bs are designated respectively as X,Y, and Z. On columns towards the left, Node Bs labeled X and Y are shownto act as serving cells before a mobility event or serving cell change.Immediately to the right of these columns are shown which Node Bs act asserving cells after the mobility event or serving cell change. Finally,to the right of the table are illustrated the cell designatorsrepresenting the Node Bs having one or more buffers corresponding to theflow flushed. As described above, if a Node B acted as a serving cellprior to the serving cell change, and also acts as a serving cell afterthe serving cell change, its buffers, e.g., a HARQ buffer, are notflushed.

TABLE 1 mobility events in SF-DC Serving cells before Serving cellsafter mobility event mobility event Cell Mobility Primary SecondaryPrimary Secondary Cell doesn't event cell cell cell cell flushed flushAnchor X Y Y X None X, Y switching (1D) Changing X Y X Z Y X secondarycell (E1D′) Changing X Y Z X Y X primary cell (E1D) Changing X Y Y Z X Yprimary cell (E1D) Changing X Y Z Y X Y primary cell (E1D) Removing X YX None Y X a serving cell (E1B) Removing X Y Y None X Y a serving cell(E1B)Changing Secondary Cell (Event 1D′)

FIG. 12 is a simplified call flow diagram illustrating some of thesignaling among nodes for an Event 1D′, which is the measurement eventfor the best primary and secondary serving cells, according to oneexample. As discussed above, the serving cells may be from one or moredifferent Node Bs and one or more different frequencies/carriers.

In the illustrated example, at time (1) Cell 1 1204 begins as the firstor primary serving cell and Cell 2 1206 begins as the second orsecondary serving cell. Cell 3 1208 is a neighboring cell for which theUE may monitor and measure its cell quality. Neighboring cells may ormay not be within the Active Set. At time (2), the UE 1202 may determinethat Cell 3 1208 exceeds Cell 2 1206 in terms of its cell quality (orCPICH E_(c)/I₀) but fails to exceed Cell 1 1202 in terms of its cellquality. Thus, the UE 1202 may transmit an RRC Measurement Reportmessage including Event 1D′ and identifying Cell 3 1208. In response, attime (3) the RNC 1210 may evaluate the RRC Measurement Report messageand transmit signaling to Cell 3 1208 over the Iub interface utilizingNBAP signaling to set up a radio link with the UE 1202. At time (4), theRNC 1210 may then transmit NBAP signaling over the Iub interface to Cell2 1206 to delete the radio link between Cell 2 1206 and the UE 1202 andflush any buffered data in a queue within Cell 2 1206 corresponding tothe flow. At time (5), the RNC 1210 may send an RRC Transport ChannelReconfiguration Request to the UE 1202 indicating a serving cell change,such that Cell 3 1208 will be the new secondary serving cell while Cell1 1204 will remain as the primary serving cell. The UE 1202 may thenrespond at time (6) with an RRC Transport Channel ReconfigurationComplete message to the RNC 1210. Thus, at time (7) HSDPA service canbegin with Cell 3 1208 as the new secondary serving cell.

In other words, when a mobility Event 1D′ has occurred, Cell 1 1204(which is the primary serving cell or Cell X in Table 1 above) continuesto serve as the primary serving cell as it is the strongest cell in theActive Set and Cell 3 1208 (which is a neighboring serving cell or CellZ in Table 1 above) is the new secondary serving cell as Cell 3 1208 isa stronger serving cell then Cell 2 1206 (the original secondary cell orCell Y in Table 1 above), but weaker than the original primary servingcell, Cell 1 1204. Since Cell 3 1208 is a stronger cell than Cell 21206, Cell 3 1208 may replace Cell 2 1206 as the secondary serving cell.As Cell 1 1204 remains as the primary serving cell following thesecondary serving cell change, the buffered data at Cell 1 1204 and atthe UE may be maintained, rather than flushed. As Cell 2 1206 has beenreplaced as the second serving cell by Cell 3 1208 and is no longeracting as a serving cell, the buffered data stored in Cell 2 1206 isflushed.

Changing Primary Cell (Event 1D)-First Example

FIG. 13 is a simplified call flow diagram illustrating some of thesignaling among nodes for an Event 1D, which is the measurement eventfor the best primary and secondary serving cells, according to oneexample. As discussed above, the serving cells may be from one or moredifferent Node Bs and one or more different frequencies/carriers.

In the illustrated example, at time (1) Cell 1 1304 begins as theprimary serving cell and Cell 2 1306 begins as the secondary servingcell. Cell 3 1308 is a neighboring cell for which the UE may monitor andmeasure its cell quality. Neighboring cells may or may not be within theActive Set. At time (2), the UE 1302 may determine that Cell 3 1308exceeds Cell 1 1304 and Cell 2 1306, in terms of its cell quality (orCPICH E_(c)/I₀) while Cell 1 1304 still exceeds the cell quality of Cell2 1306. Thus, the UE 1302 may transmit an RRC Measurement Report messageincluding Event 1D and identifying that the cell quality of Cell 3 1308exceeds the cell quality of Cell 1 1304 and Cell 2 1306 while the cellquality of Cell 1 1304 still exceeds the cell quality of Cell 2 1306. Inresponse, at time (3) the RNC 1310 may evaluate the RRC MeasurementReport message and transmit signaling to Cell 3 1308 over the Iubinterface utilizing NBAP signaling to set up a radio link with the UE1302. At time (4), the RNC 1310 may then transmit NBAP signaling overthe Iub interface to Cell 2 1306 to delete the radio link between Cell 21306 and the UE 1302 and flush any buffered data in Cell 2 1306corresponding to the flow. At time (5), the RNC 1310 may send an RRCTransport Channel Reconfiguration Request to the UE 1302 indicating aserving cell change, such that Cell 3 1308 will be the new primaryserving cell while Cell 1 1304 will be the new secondary serving cell.The UE 1302 may then respond at time (6) with an RRC Transport ChannelReconfiguration Complete message to the RNC 1310. Thus, at time (7)HSDPA service can begin with Cell 3 1308 as the new primary serving celland Cell 1 1304 as the new secondary serving cell. As Cell 1 1304remains as a serving cell, the buffered data at Cell 1 1304 and at theUE may be maintained, i.e. not flushed.

In other words, when a mobility Event 1D has occurred, Cell 1 1304(which is the primary serving cell or Cell X in Table 1 above) and Cell2 1306 the original secondary cell or Cell Y in Table 1 above) arereplaced. Cell 1 1304 is replaced with Cell 3 1308 (which is aneighboring serving cell or Cell Z in Table 1 above) and Cell 1 1304,which is now the second strongest cell, becomes the new secondaryserving cell and replaces Cell 2 1306. That is, Cell 3 1308 becomes thenew primary serving cell replacing Cell 1 1304, while Cell 1 1304becomes the new secondary serving cell replacing Cell 2 1306. As Cell 11304 is serving as the secondary serving cell, the buffered data at Cell1 1304 and at the UE may be maintained, rather than flushed and as Cell2 1306 has been replaced as the second serving cell by Cell 1 1304 andis no longer acting as a serving cell, the buffered data stored in Cell2 1306 is flushed.

Changing Primary Cell (Event 1D) - Second Example

FIG. 14 is a simplified call flow diagram illustrating some of thesignaling among nodes for an Event 1D, which is the measurement eventfor the best primary and secondary serving cells, according to oneexample. As discussed above, the serving cells may be from one or moredifferent Node Bs and one or more different frequencies/carriers.

In the illustrated example, at time (1) Cell 1 1404 begins as theprimary serving cell and Cell 2 1406 begins as the secondary servingcell. Cell 3 1408 is a neighboring cell for which the UE may monitor andmeasure its cell quality. Neighboring cells may or may not be within theActive Set. At time (2), the UE 1402 may determine that Cell 3 1408exceeds Cell 1 1404 in terms of its cell quality (or CPICH E_(c)/I₀)while Cell 2 1406 still exceeds the cell quality of Cell 3 1408. Thus,the UE 1402 may transmit an RRC Measurement Report message includingEvent 1D and identifying that the cell quality of Cell 3 1408 exceedsthe cell quality of Cell 1 1404 while the cell quality of Cell 2 1406still exceeds the cell quality of Cell 3 1408. In response, at time (3)the RNC 1410 may evaluate the RRC Measurement Report message andtransmit signaling to Cell 3 1408 over the Iub interface utilizing NBAPsignaling to set up a radio link with the UE 1402. At time (4), the RNC1410 may then transmit NBAP signaling over the Iub interface to Cell 11404 to delete the radio link between Cell 1 1406 and the UE 1402 andflush any buffered data in Cell 1 1406 corresponding to the flow as itis no longer acting as a serving cell. At time (5), the RNC 1410 maysend an RRC Transport Channel Reconfiguration Request to the UE 1402indicating a serving cell change, such that Cell 2 1406, will be the newprimary serving cell while Cell 3 1408 will be the new secondary servingcell. The UE 1402 may then respond at time (6) with an RRC TransportChannel Reconfiguration Complete message to the RNC 1410. Thus, at time(7) HSDPA service can begin with Cell 2 1406 as the new primary servingcell and Cell 3 1408 as the new secondary serving cell. As Cell 2 1406remains as a serving cell, the buffered data at Cell 2 1406 and at theUE may be maintained, i.e. not flushed.

In other words, when a mobility Event 1D has occurred, Cell 1 1404(which is the primary serving cell or Cell X in Table 1 above) and Cell2 1406 the original secondary cell or Cell Y in Table 1 above) arereplaced. Cell 1 1404 is replaced with Cell 2 1406 and Cell 3 1408(which is the neighboring serving cell or Cell Z in Table 1 above) whichis now the second strongest cell, becomes the new secondary serving celland replaces Cell 2 1406. That is, Cell 2 1406 becomes the new primaryserving cell replacing Cell 1 1404 while Cell 3 1408 becomes the newsecondary serving cell replacing Cell 2 1406. As Cell 1 1404 is nolonger serving the UE, the buffered data at Cell 1 1404 is flushed,while the buffered data stored in Cell 2 1406 and at the UE may bemaintained.

Changing Primary Cell (Event 1D) - Third Example

FIG. 15 is a simplified call flow diagram illustrating some of thesignaling among nodes for an Event 1D, which is the measurement eventfor the best primary and secondary serving cells, according to oneexample. As discussed above, the serving cells may be from one or moredifferent Node Bs and one or more different frequencies/carriers.

In the illustrated example, at time (1) Cell 1 1504 begins as theprimary serving cell and Cell 2 1506 begins as the secondary servingcell. Cell 3 1508 is a neighboring cell for which the UE may monitor andmeasure its cell quality. Neighboring cells may or may not be within theActive Set. At time (2), the UE 1502 may determine that Cell 3 1508exceeds Cell 1 1504 and Cell 2 1506 in terms of its cell quality (orCPICH E_(c)/I₀) while Cell 2 1506 now exceeds the cell quality of Cell 11502. Thus, the UE 1502 may transmit an RRC Measurement Report messageincluding Event 1D and identifying that the cell quality of Cell 3 1508exceeds the cell quality of Cell 1 1504 and Cell 2 1506 while the cellquality of Cell 2 1506 now exceeds the cell quality of Cell 1 1508. Inresponse, at time (3) the RNC 1510 may evaluate the RRC MeasurementReport message and transmit signaling to Cell 3 1508 over the Iubinterface utilizing NBAP signaling to set up a radio link with the UE1502. At time (4), the RNC 1510 may then transmit NBAP signaling overthe Iub interface to Cell 1 1504 to delete the radio link between Cell 11504 and the UE 1502 and flush any buffered data in Cell 1 1502corresponding to the flow as Cell 1 1502 is no longer acting as aserving cell. At time (5), the RNC 1510 may send an RRC TransportChannel Reconfiguration Request to the UE 1502 indicating a serving cellchange, such that Cell 3 1508 will be the new primary serving cell whileCell 2 1506 will remain as the secondary serving cell. The UE 1502 maythen respond at time (6) with an RRC Transport Channel ReconfigurationComplete message to the RNC 1510. Thus, at time (7) HSDPA service canbegin with Cell 3 1508 as the new primary serving cell and Cell 2 1506remaining as the secondary serving cell. As Cell 2 1506 remains as aserving cell, the buffered data at Cell 2 1506 and at the UE may bemaintained, i.e. not flushed.

In other words, when a mobility Event 1D has occurred, Cell 1 1504(which is the primary serving cell or Cell X in Table 1 above) isreplaced and Cell 2 1506 (which is the original secondary cell or Cell Yin Table 1 above) remains unchanged. Cell 1 1504 is replaced with Cell 31508 (which is the neighboring serving cell or Cell Z in Table 1 above)which is now the strongest cell while Cell 2 1506 remains as thesecondary serving cell. That is, Cell 3 1508 becomes the new primaryserving cell replacing Cell 1 1504 while Cell 2 1506 remains as thesecondary serving cell. As Cell 1 1504 is no longer serving the UE, thebuffered data at Cell 1 1504 is flushed, while the buffered data storedin Cell 2 1506 and at the UE may be maintained.

Removing a Serving Cell (Event 1B) - First Example

FIG. 16 is a simplified call flow diagram illustrating some of thesignaling among nodes for an Event 1B, which is the measurement eventfor the best primary serving cell, according to one example. Asdiscussed above, the serving cells may be from one or more differentNode Bs and one or more different frequencies/carriers.

In the illustrated example, at time (1) Cell 1 1604 begins as theprimary serving cell and Cell 2 1606 begins as the secondary servingcell. At time (2), the UE 1602 may determine that Cell 1 1604 stillexceeds all other cells in terms of its cell quality (or CPICHE_(c)/I₀). Thus, the UE 1602 may transmit an RRC Measurement Reportmessage including Event 1B and identifying that the cell quality of Cell1 1604 still exceeds the cell quality of Cell 2 1606. Additionally, thecell quality of Cell 2 1606 may be determined to exceed a predeterminedthreshold, fall below a predetermined threshold or leave a reportingrange. In response, at time (3) the RNC 1610 may evaluate the RRCMeasurement Report message and transmit NBAP signaling over the Iubinterface to Cell 2 1606 to delete the radio link between Cell 2 1606and the UE 1602 and flush any buffered data in Cell 2 1606 correspondingto the flow.

In other words, when a mobility Event 1B has occurred, Cell 1 1604(which is the primary serving cell or Cell X in Table 1 above) remainsas the primary serving cell and Cell 2 1606 (which is the originalsecondary serving cell or Cell Y in Table 1 above) is removed, i.e. itslink with the UE is deleted. A new secondary serving cell is notassigned. As Cell 2 1606 is no longer serving the UE, the buffered dataat Cell 2 1606 is flushed, while the buffered data stored in Cell 1 1604and at the UE may be maintained.

Removing a Serving Cell (Event 1B) - Second Example

FIG. 17 is a simplified call flow diagram illustrating some of thesignaling among nodes for an Event 1B, which is the measurement eventfor the best primary serving cell, according to one example. Asdiscussed above, the serving cells may be from one or more differentNode Bs and one or more different frequencies/carriers.

In the illustrated example, at time (1) Cell 1 1704 begins as theprimary serving cell and Cell 2 1706 begins as the secondary servingcell. At time (2), the UE 1702 may determine that Cell 2 1706 nowexceeds Cell 1 1704 and all other cells in terms of its cell quality (orCPICH E_(c)/I₀). Thus, the UE 1702 may transmit an RRC MeasurementReport message including Event 1B and identifying that the cell qualityof Cell 2 1706 now exceeds the cell quality of Cell 1 1704.Additionally, the cell quality of Cell 1 1704 may be determined toexceed a predetermined threshold, fall below a predetermined thresholdor leave a reporting range. In response, at time (3) the RNC 1710 mayevaluate the RRC Measurement Report message and transmit NBAP signalingover the Iub interface to Cell 1 1704 to delete the radio link betweenCell 1 1704 and the UE 1702 and flush any buffered data in Cell 7 1704corresponding to the flow. At time (4), the RNC 1710 may send an RRCTransport Channel Reconfiguration Request to the UE 1702 indicating aserving cell change, such that Cell 2 1706 will be the new primaryserving cell and that the link with Cell 1 1704 has been deleted. The UE1702 may then respond at time (5) with an RRC Transport ChannelReconfiguration Complete message to the RNC 1710. Thus, at time (6)HSDPA service can begin with Cell 2 1706 as the new primary servingcell. As Cell 2 1706 remains as a serving cell, the buffered data atCell 2 1706 and at the UE may be maintained, i.e. not flushed.

In other words, when a mobility Event 1B has occurred, Cell 2 1706(which is the secondary serving cell or Cell Y in Table 1 above) becomesthe new primary serving cell and Cell 1 1704 (which is the originalprimary serving cell or Cell X in Table 1 above) is removed, i.e. itslink with the UE is deleted. A new secondary serving cell is notassigned. As Cell 1 1704 is no longer serving the UE, the buffered dataat Cell 1 1704 is flushed, while the buffered data stored in Cell 2 1706and at the UE may be maintained.

FIG. 18 is a flow chart illustrating a process, operational at a RNC ina UTRAN, for reducing data loss during a serving cell change in aMulti-flow HSPDA communication network.

First, a downlink flow may be transmitted from the RNC to a userequipment (UE) utilizing at least a first base station and a second basestation to provide a first serving cell and a second serving cell,respectively, to be aggregated at the UE 1802. The RNC may then receivea measuring report from the UE ranking the cell qualities of the firstserving cell and the second serving cell 1804. The cell qualities of thefirst serving cell and the second serving cell may be ranked from thestrongest serving cell to the weakest serving cell by the UE.

Next, the RNC may perform a serving cell change where the first basestation or the second base station continues to act as a serving cell tothe UE 1806. The acting serving cell may be selected based on thestrongest cell quality from the ranked cell qualities and the actingserving cell may be the primary serving cell and the non-selectedserving cell may be the secondary serving cell.

The measuring report may also include rankings of the cell qualities ofone or more neighboring cells, provided by one or more base stations,upon an occurrence of a mobility event. A neighboring cell may be addedto an active set associated with the UE when the cell quality of theneighboring cell is stronger than the cell quality of the primaryserving cell or the secondary serving cell upon the occurrence of themobility event.

Next, instructions may be sent by the RNC to the acting serving cell tomaintain data corresponding to the flow before the serving cell changewithin a queue at the acting serving cell for transmission to the UEafter the serving cell change 1808.

A serving cell change may occur as a result of a mobility event. Asdiscussed above, a mobility event may include, but is not limited to,(1) the UE measurements of E_(c)/I₀ for a particular cell reaches aparticular threshold and maintains that level for a certain time suchthat it may be appropriate to add the cell to the Active Set; (2) the UEmeasurements of E_(c)/I₀ for a particular cell falls below a particularor predetermined threshold, and maintains that level for a certain timesuch that it may be appropriate to remove the cell from the Active Set areporting; and (3) a neighbor cell (which may or may not be within theActive Set) exceeds the quality of the serving HS-DSCH cell according tothe UE measurements of E_(c)/I₀.

Several aspects of a telecommunications system have been presented withreference to a W-CDMA system. As those skilled in the art will readilyappreciate, various aspects described throughout this disclosure may beextended to other telecommunication systems, network architectures andcommunication standards.

By way of example, various aspects may be extended to other UMTS systemssuch as TD-SCDMA and TD-CDMA. Various aspects may also be extended tosystems employing Long Term Evolution (LTE) (in FDD, TDD, or bothmodes), LTE-Advanced (LTE-A) (in FDD, TDD, or both modes), CDMA2000,Evolution-Data Optimized (EV-DO), Ultra Mobile Broadband (UMB), IEEE802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Ultra-Wideband (UWB),Bluetooth, and/or other suitable systems. The actual telecommunicationstandard, network architecture, and/or communication standard employedwill depend on the specific application and the overall designconstraints imposed on the system.

The previous description is provided to enable any person skilled in theart to practice the various aspects described herein. Variousmodifications to these aspects will be readily apparent to those skilledin the art, and the generic principles defined herein may be applied toother aspects. Thus, the claims are not intended to be limited to theaspects shown herein, but is to be accorded the full scope consistentwith the language of the claims, wherein reference to an element in thesingular is not intended to mean “one and only one” unless specificallyso stated, but rather “one or more.” Unless specifically statedotherwise, the term “some” refers to one or more. A phrase referring to“at least one of” a list of items refers to any combination of thoseitems, including single members. As an example, “at least one of: a, b,or c” is intended to cover: a; b; c; a and b; a and c; b and c; and a, band c. All structural and functional equivalents to the elements of thevarious aspects described throughout this disclosure that are known orlater come to be known to those of ordinary skill in the art areexpressly incorporated herein by reference and are intended to beencompassed by the claims. Moreover, nothing disclosed herein isintended to be dedicated to the public regardless of whether suchdisclosure is explicitly recited in the claims. No claim element is tobe construed under the provisions of 35 U.S.C. §112, sixth paragraph,unless the element is expressly recited using the phrase “means for” or,in the case of a method claim, the element is recited using the phrase“step for.”

The invention claimed is:
 1. A method of wireless communication,comprising: transmitting a downlink flow to a user equipment (UE)utilizing at least a first base station and a second base station toprovide a first serving cell and a second serving cell, respectively, tobe aggregated at the UE; performing a serving cell change by replacingthe first serving cell or the second serving cell with a third cell whena quality of the third cell is greater than the first serving cell andthe second serving cell, wherein the first base station or the secondbase station continues to act as a serving cell to the UE after theserving cell change; and forgoing to instruct the acting serving cell toflush data corresponding to the flow, so that the acting serving cellmaintains the data corresponding to the flow before the serving cellchange within a queue at the acting serving cell for transmission fromthe acting serving cell to the UE directly after the serving cellchange.
 2. The method of claim 1, further comprising: receiving a reportfrom the UE ranking cell qualities of the first serving cell and thesecond serving cell, where the acting serving cell is selected based onstrongest cell quality from the ranked cell qualities; and wherein theacting serving cell is a primary serving cell and the non-selectedserving cell is the secondary serving cell.
 3. The method of claim 2,wherein the report further includes ranking of the cell qualities of oneor more neighboring cells including the third cell, provided by one ormore base stations, upon an occurrence of a mobility event; and whereinthe third cell is added to an active set associated with the UE when thecell quality of the third cell is stronger than the cell quality of theprimary serving cell or the secondary serving cell upon the occurrenceof the mobility event.
 4. The method of claim 3, further comprising:performing a primary serving cell change by replacing the primaryserving cell with the third cell when the cell quality of the third cellis greater than the cell quality of the primary serving cell, the thirdcell becoming a new primary serving cell; performing a secondary servingcell change by replacing the secondary serving cell with the primaryserving cell when the cell quality of the primary serving cell isgreater than the cell quality of the secondary serving cell, the primaryserving cell becoming a new secondary serving cell; maintaining the datacorresponding to the flow within a queue at the new primary servingcell; and flushing the data corresponding to the flow within a queue atthe secondary serving cell.
 5. The method of claim 3, furthercomprising: performing a primary serving cell change by replacing theprimary serving cell with the secondary serving cell when the cellquality of the secondary serving cell is greater than the cell qualityof the primary serving cell, the secondary serving cell becoming a newprimary serving cell; performing a secondary serving cell change byreplacing the secondary serving cell with the third cell when the cellquality of the third cell is greater than the cell quality of thesecondary serving cell, the third cell becoming a new secondary servingcell; maintaining the data corresponding to the flow within a queue atthe new primary serving cell; and flushing the data corresponding to theflow within a queue at the secondary serving cell.
 6. The method ofclaim 3, further comprising: performing a primary serving cell change byreplacing the primary serving cell with the third cell when the cellquality of the third cell is greater than the cell quality of theprimary serving cell, the third cell becoming a new primary servingcell; maintaining the data corresponding to the flow within a queue atthe new primary serving cell; and flushing the data corresponding to theflow within a queue at the primary serving cell.
 7. The method of claim3, further comprising: removing the secondary serving cell from theactive set associated with the UE when the cell quality of the secondaryserving cell is below a predetermined threshold; and flushing the datacorresponding to the flow within a queue at the secondary serving cell.8. The method of claim 3, further comprising: performing a primaryserving cell change by replacing the primary serving cell with thesecondary serving cell when the cell quality of the secondary servingcell is greater than the cell quality of the primary serving cell, thesecondary serving cell becoming a new primary serving cell; removing theprimary serving cell from the active set associated with the UE when thecell quality of the primary serving cell is below a predeterminedthreshold; and flushing the data corresponding to the flow within aqueue at the primary serving cell.
 9. The method of claim 3, wherein themobility event is a UE measurement of E_(c)/I₀ for a particular cellthat reaches a predetermined threshold and maintains the predeterminedthreshold for a predetermined time.
 10. The method of claim 3, whereinthe mobility event is a UE measurement of E_(c)/I₀ for a particularserving cell falls that below a predetermined threshold and maintainsthe predetermined threshold for a predetermined time.
 11. An apparatusfor wireless communication, comprising: means for transmitting adownlink flow to user equipment (UE) utilizing at least a first basestation and a second base station to provide a first serving cell and asecond serving cell, respectively, to be aggregated at the UE; means forperforming a serving cell change by replacing the first serving cell orthe second serving cell with a third cell when a quality of the thirdcell is greater than the first serving cell and the second serving cell,wherein the first base station or the second base station continues toact as a serving cell to the UE after the serving cell change; and meansfor forgoing to instruct the acting serving cell to flush datacorresponding to the flow, so that the acting serving cell maintains thedata corresponding to the flow before the serving cell change within aqueue at the acting serving cell for transmission from the actingserving cell to the UE directly after the serving cell change.
 12. Theapparatus of claim 11, further comprising: means for receiving a reportfrom the UE ranking cell qualities of the first serving cell and thesecond serving cell, where the acting serving cell is selected based onstrongest cell quality from the ranked cell qualities; and wherein theacting serving cell is a primary serving cell and the non-selectedserving cell is the secondary serving cell.
 13. The apparatus of claim12, wherein the report further includes ranking of the cell qualities ofone or more neighboring cells including the third cell, provided by oneor more base stations, upon an occurrence of a mobility event; andwherein a the third cell is added to an active set associated with theUE when the cell quality of the third cell is stronger than the cellquality of the primary serving cell or the secondary serving cell uponthe occurrence of the mobility event.
 14. The apparatus of claim 13,further comprising: means for performing a primary serving cell changeby replacing the primary serving cell with the third cell when the cellquality of the third cell is greater than the cell quality of theprimary serving cell, the third cell becoming a new primary servingcell; means for performing a secondary serving cell change by replacingthe secondary serving cell with the primary serving cell when the cellquality of the primary serving cell is greater than the cell quality ofthe secondary serving cell, the primary serving cell becoming a newsecondary serving cell; means for maintaining the data corresponding tothe flow within a queue at the new primary serving cell; and means forflushing the data corresponding to the flow within a queue at thesecondary serving cell.
 15. The apparatus of claim 13, furthercomprising: means for performing a primary serving cell change byreplacing the primary serving cell with the secondary serving cell whenthe cell quality of the secondary serving cell is greater than the cellquality of the primary serving cell, the secondary serving cell becominga new primary serving cell; means for performing a secondary servingcell change by replacing the secondary serving cell with the third cellwhen the cell quality of the third cell is greater than the cell qualityof the secondary serving cell, the third cell becoming a new secondaryserving cell; means for maintaining the data corresponding to the flowwithin a queue at the new primary serving cell; and means for flushingthe data corresponding to the flow within a queue at the secondaryserving cell.
 16. The apparatus of claim 13, further comprising: meansfor performing a primary serving cell change by replacing the primaryserving cell with the third cell when the cell quality of the third cellis greater than the cell quality of the primary serving cell, the thirdcell becoming a new primary serving cell; means for maintaining the datacorresponding to the flow within a queue at the new primary servingcell; and means for flushing the data corresponding to the flow within aqueue at the primary serving cell.
 17. The apparatus of claim 13,further comprising: means for removing the secondary serving cell fromthe active set associated with the UE when the cell quality of thesecondary serving cell is below a predetermined threshold; and means forflushing the data corresponding to the flow within a queue at thesecondary serving cell.
 18. The apparatus of claim 13, furthercomprising: means for performing a primary serving cell change byreplacing the primary serving cell with the secondary serving cell whenthe cell quality of the secondary serving cell is greater than the cellquality of the primary serving cell, the secondary serving cell becominga new primary serving cell; means for removing the primary serving cellfrom the active set associated with the UE when the cell quality of theprimary serving cell is below a predetermined threshold; and means forflushing the data corresponding to the flow within a queue at theprimary serving cell.
 19. A computer program product, comprising: anon-transitory computer-readable medium comprising: instructions forcausing a computer to transmit a downlink flow to user equipment (UE)utilizing at least a first base station and a second base station toprovide a first serving cell and a second serving cell, respectively, tobe aggregated at the UE; instructions for causing a computer to performa serving cell change by replacing the first serving cell or the secondserving cell with a third cell when a quality of the third cell isgreater than the first serving cell and the second serving cell, whereinthe first base station or the second base station continues to act as aserving cell to the UE after the serving cell change; and instructionsfor causing a computer to forgo to instruct the acting serving cell toflush data corresponding to the flow, so that the acting serving cellmaintains the data corresponding to the flow before the serving cellchange within a queue at the acting serving cell for transmission fromthe acting serving cell to the UE directly after the serving cellchange.
 20. The computer program product of claim 19, wherein thecomputer-readable medium further comprises: instructions for causing acomputer to receive a report from the UE ranking cell qualities of thefirst serving cell and the second serving cell, where the acting servingcell is selected based on strongest cell quality from the ranked cellqualities; and wherein the acting serving cell is a primary serving celland the non-selected serving cell is the secondary serving cell.
 21. Theapparatus of claim 20, wherein the report further includes ranking ofthe cell qualities of one or more neighboring cells including the thirdcell, provided by one or more base stations, upon an occurrence of amobility event; and wherein the third cell is added an active setassociated with the UE when the cell quality of the third cell isstronger than the cell quality of the primary serving cell or thesecondary serving cell upon the occurrence of the mobility event. 22.The computer program product of claim 21, wherein the computer-readablemedium further comprises: instructions for causing a computer to performa primary serving cell change by replacing the primary serving cell withthe third cell when the cell quality of the third cell is greater thanthe cell quality of the primary serving cell, the third cell becoming anew primary serving cell; instructions for causing a computer to performa secondary serving cell change by replacing the secondary serving cellwith the primary serving cell when the cell quality of the primaryserving cell is greater than the cell quality of the secondary servingcell, the primary serving cell becoming a new secondary serving cell;instructions for causing a computer to maintain the data, after cellchange, corresponding to the flow within a queue at the new primaryserving cell; and instructions for causing a computer to flush the datacorresponding to the flow within a queue at the secondary serving cell.23. The computer program product of claim 21, wherein thecomputer-readable medium further comprises: instructions for causing acomputer to perform a primary serving cell change by replacing theprimary serving cell with the secondary serving cell when the cellquality of the secondary serving cell is greater than the cell qualityof the primary serving cell, the secondary serving cell becoming a newprimary serving cell; instructions for causing a computer to perform asecondary serving cell change by replacing the secondary serving cellwith the third cell when the cell quality of the third cell is greaterthan the cell quality of the secondary serving cell, the third cellbecoming a new secondary serving cell; instructions for causing acomputer to maintain the data corresponding to the flow within a queueat the new primary serving cell; and instructions for causing a computerto flush the data corresponding to the flow within a queue at thesecondary serving cell.
 24. The computer program product of claim 21,wherein the computer-readable medium further comprises: instructions forcausing a computer to perform a primary serving cell change by replacingthe primary serving cell with the third cell when the cell quality ofthe third cell is greater than the cell quality of the primary servingcell, the third cell becoming a new primary serving cell; instructionsfor causing a computer to maintain the data corresponding to the flowwithin a queue at the new primary serving cell; and instructions forcausing a computer to flush the data corresponding to the flow within aqueue at the primary serving cell.
 25. The computer program product ofclaim 21, wherein the computer-readable medium further comprises:instructions for causing a computer to remove the secondary serving cellfrom the active set associated with the UE when the cell quality of thesecondary serving cell is below a predetermined threshold; andinstructions for causing a computer to flush the data corresponding tothe flow within a queue at the secondary serving cell.
 26. The computerprogram product of claim 21, wherein the computer-readable mediumfurther comprises: instructions for causing a computer to perform aprimary serving cell change by replacing the primary serving cell withthe secondary serving cell when the cell quality of the secondaryserving cell is greater than the cell quality of the primary servingcell, the secondary serving cell becoming a new primary serving cell;instructions for causing a computer to remove the primary serving cellfrom the active set associated with the UE when the cell quality of theprimary serving cell is below a predetermined threshold; andinstructions for causing a computer to flush the data corresponding tothe flow within a queue at the primary serving cell.
 27. An apparatusfor wireless communication, comprising: at least one processor; and amemory coupled to the at least one processor, wherein the at least oneprocessor is configured to: transmit a downlink flow to user equipment(UE) utilizing at least a first base station and a second base stationto provide a first serving cell and a second serving cell, respectively,to be aggregated at the UE; perform a serving cell change by replacingthe first serving cell or the second serving cell with a third cell whena quality of the third cell is greater than the first serving cell andthe second serving cell, wherein the first base station or the secondbase station continues to act as a serving cell to the UE after theserving cell change; and forgo to instruct the acting serving cell toflush data corresponding to the flow, so that the acting serving cellmaintains the data corresponding to the flow before the serving cellchange within a queue at the acting serving cell for transmission fromthe acting serving cell to the UE directly after the serving cellchange.
 28. The apparatus of claim 27, wherein the at least oneprocessor is further configured to: receive a report from the UE rankingcell qualities of the first serving cell and the second serving cell,where the acting serving cell is selected based on strongest cellquality from the ranked cell qualities; and wherein the acting servingcell is a primary serving cell and the non-selected serving cell is thesecondary serving cell.
 29. The apparatus of claim 28, wherein thereport further includes ranking of the cell qualities of one or moreneighboring cells including the third cell, provided by one or more basestations, upon an occurrence of a mobility event; and wherein the thirdcell is added an active set associated with the UE when the cell qualityof the third cell is stronger than the cell quality of the primaryserving cell or the secondary serving cell upon the occurrence of themobility event.
 30. The apparatus of claim 29, wherein the at least oneprocessor is further configured to: perform a primary serving cellchange by replacing the primary serving cell with the third cell whenthe cell quality of the third cell is greater than the cell quality ofthe primary serving cell, the third cell becoming a new primary servingcell; perform a secondary serving cell change by replacing the secondaryserving cell with the primary serving cell when the cell quality of theprimary serving cell is greater than the cell quality of the secondaryserving cell, the primary serving cell becoming a new secondary servingcell; maintain the data corresponding to the flow within a queue at thenew primary serving cell; and flush the data corresponding to the flowwithin a queue at the secondary serving cell.
 31. The apparatus of claim29, wherein the at least one processor is further configured to: performa primary serving cell change by replacing the primary serving cell withthe secondary serving cell when the cell quality of the secondaryserving cell is greater than the cell quality of the primary servingcell, the secondary serving cell becoming a new primary serving cell;perform a secondary serving cell change by replacing the secondaryserving cell with the third cell when the cell quality of the third cellis greater than the cell quality of the secondary serving cell, thethird cell becoming a new secondary serving cell; maintain the datacorresponding to the flow within a queue at the new primary servingcell; and flush the data corresponding to the flow within a queue at thesecondary serving cell.
 32. The apparatus of claim 29, wherein the atleast one processor is further configured to: perform a primary servingcell change by replacing the primary serving cell with the third cellwhen the cell quality of the third cell is greater than the cell qualityof the primary serving cell, the third cell becoming a new primaryserving cell; maintain the data corresponding to the flow within a queueat the new primary serving cell; and flush the data corresponding to theflow within a queue at the primary serving cell.
 33. The apparatus ofclaim 29, wherein the at least one processor is further configured to:remove the secondary serving cell from the active set associated withthe UE when the cell quality of the secondary serving cell is below apredetermined threshold; and flush the data corresponding to the flowwithin a queue at the secondary serving cell.
 34. The apparatus of claim29, wherein the at least one processor is further configured to: performa primary serving cell change by replacing the primary serving cell withthe secondary serving cell when the cell quality of the secondaryserving cell is greater than the cell quality of the primary servingcell, the secondary serving cell becoming a new primary serving cell;remove the primary serving cell from the active set associated with theUE when the cell quality of the primary serving cell is below apredetermined threshold; and flush the data corresponding to the flowwithin a queue at the primary serving cell.